TYPES OF SCREW AND WAYS OF IDENTIFYING （类型的螺丝和识别的方法）.pdf

TYPES OF SCREW AND WAYS OF IDENTIFYING THEM Things to look at when considering which type of screw is needed? • Type of drive • Shape of head • Type of thread • Type of point • Length of screw • Length of thread • Colour of screw Types of screw head and therefore screwdriver needed? • Hex head • Has Allen key type socket on head, uses hex screwdriver • Slot head • Has single slot head, uses flat blade screwdriver • Cruciate head • Has cross head, uses + head screwdriver Shapes of screw head Spherical Head Conical Head Threaded Conical Head - Head is rounded - Found in Sherman self - Locking screws - Found in Cortical Cancellous tapping screws - Screw thread on head screws engages locking plate - Works with compression plates Types of thread • Pitch is the distance between the ridges in a screw thread • Cortical thread – fine shallow thread Found in Cortical Cortical Self tapping Screws • Cancellous thread – deep wide thread Found in cancellous screws full part threaded Types of screw point –Self Tapping or Non-Self Tapping • All screws need a thread to engage in bone when they are tightened, which stops them pulling out. • Either the screw cuts its own thread as it is driven in – self tapping screw • Or a separate tap is used to cut the thread for a non self tapping screw • Self tapping screw tips have 1 or more ‘flutes’ in the tip which cut the thread as the screw is driven in • Some cancellous screws (4mm) have a self tapping ‘pigtail’ sharp point • Non self tapping screws have a blunter, more rounded tip and no flutes Self Tapping Non-Self Tapping Measuri